The present invention relates to a process for the preparation of meso-1,2,3,4-tetrachlorobutane by chlorination of trans-1,4-dichlorobutene-2. More particularly the present invention relates to a catalytic chlorination process in liquid phase.
2,3-DICHLORO-1,3-BUTADIENE, WHICH IS A VALUABLE MONOMER USED FOR POLYMERIZATIONS, E.G., THE COPOLYMERIZATION WITH CHLOROPRENE (2-CHLORO-1,3-BUTADIENE) TO PRODUCE CRYSTALLIZATION RESISTANT TYPES OF RUBBER IS CONVENIENTLY MADE BY THE DEHYDROCHLORINATION OF MESO-1,2,3,4-TETRACHLOROBUTANE. Although the 2,3-dichloro-1,3-butadiene may be made from the dl-racemic mixture of 1,2,3,4-tetrachlorobutane the meso-isomer produces higher yield and fewer undesirable by-products.
In preparing meso-1,2,3,4-tetrachlorobutane from dichlorobutenes in a liquid phase chlorination process, there are produced, in addition to the desired meso-isomer, dl-isomer and a proportion of chlorinated materials designated as heavy ends and light ends. These heavy ends are generally more highly chlorinated products such as the pentachlorobutanes. The light ends are less chlorinated products such as the trichlorinated C.sub.4 's. The formation of dl-isomer and heavy and light ends is undesirable in that these materials represent a yield loss and are undesirable contaminants in the desired meso-1,2,3,4-tetrachlorobutane product.
Known methods for preparing meso-1,2,3,4-tetrachlorobutane from dichlorobutenes in a liquid phase chlorination process have been generally unsatisfactory. Non-catalytic process, such as those disclosed in Japanese Pat. No. 38,802 (1970) and in the Journal of the American Chemical Society 73, 244- 6 (1951), require extremely low temperatures of from 0.degree. C. to about -30.degree. C. and are, therefore, generally undesirable economically. Other processes for carrying out the chlorination reaction at moderate temperatures in the range of from about 50.degree. C.-150.degree. C. involve the use of a catalyst, for example, the processes disclosed in French Pat. No. 1,401,077 (titanium tetrachloride catalysts), French Pat. No. 1,401,078 (pyridine catalysts), and U.S. Pat. No. 2,445,729 (ferric chloride or antimony pentachloride catalysts). All of these processes are generally unsatisfactory in that there are produced a large proportion of heavy ends material and an undesirably large proportion of the dl-isomer. These catalytic processes are additionally undesirable due to the presence of the metallic catalyst.
Recently improved processes have been described in U.S. Pat. No. 3,901,950 (oxygen and dissolved chloride ion), U.S. Pat. No. 3,980,725 (absence of oxygen in the presence of nitric oxide) and U.S. Pat. No. 3,932,544 (controlled chlorine reaction rate), all of which have succeeded in reducing the dl-isomer in the chlorination reaction.
The light ends represent lost production of the desirable tetrachlorbutane, i.e., particularly the desirable meso-isomer.
The advantages of the present invention include reduced light ends from the chlorination of trans-1,4-dichlorobutene-2; improved reaction rate time trends; lower heavy ends and increased yield of meso-1,2,3,4-tetrachlorobutane. A particular feature of the present invention is that the present catalyst may be used in combination with other improvements in the art.